Polymer mixtures and articles formed therefrom

Abstract: The invention relates to polymer mixtures comprising a first polyalkylene phthalate, for example, polybutylene terephthalate, and a second polyalkylene phthalate and/or a thermoplastic elastomer and phosphorus compounds. It has been found that, with regard to the crystallisation behaviour, the addition of certain nucleating agents (namely talcum or carbon black) show a synergistic effect with certain phosporus compounds.

Description: The invention relates to a polymer mixture comprising A. a first polyalkylene phthalate which comprises more than 35 mol% of units derived from 1,4-butanediol and which comprises more than 35 mol% of units derived from terephthalic acid; and B. B1 a second polyalkylene phthalate which comprises less than 15 mol% of units derived from 1,4-butanediol; or B2 a thermoplastic elastomer selected from a polyether ester block copolymer, a polyester ester urethane and a polyether imide ester or a mixture thereof; or B3 a mixture of B1 and B2; and C. a certain type of transesterification inhibitor as indicated hereinafter, and D. a certain type of nucleating agent as indicated hereinafter. The invention also relates to articles formed from a polymer mixture according to the invention. Blends of two polyesters are generally known. EP-A-0 604 074 published on June 29, 1994 describes blends of a relatively low molecular weight polybutylene terephthalate resin, a relatively high molecular weight polyester resin and a melt viscosity stabilizer. The known blends may comprise further additives like glass fibers, talc, mica, clay of mixtures thereof. The high molecular weight resin and the melt viscosity stabilizers can be chosen among a variety of possibilities. EP-A-0 604 080 published on June 29, 1994 describes compositions which comprise polybutylene terephthalate and/or polyethylene terephthalate, a polycarbonate, a stabilizer and an inorganic filler selected from barium sulfate, strontium sulfate, zirconium oxide and zinc sulfate. EP-A-0 609 538 published on August 10, 1994 describes polymer mixtures comprising two polyesters and a transesterification inhibitor. The known mixtures may comprise carbon black. US-A-4,111,892 describes compositions comprising polybutylene terephthalate (which can be admixed with another polymer which can be polyethylene terephthalate), a flame reatardant combination of a halogen containing compound, hydrated silica and a reinforcing filler. The reinforcing filler can comprise talc and a second reinforcing filler. The talc and the hydated silica are added to improve the electrical characteristics of the composition. GB-A-1 060 401 describes the use of phosphorus compounds like for example diammonium hydrogen phosphate, ammonium dihydrogen phosphate, magnesium hydrogen phosphate and manganese hydrogen phosphate. The hydrogen phosphates just mentioned have for their disadvantage that they negatively influence the mechanical properties, for example, the tensile strength and the impact strength. The thermal properties, for example, HDT (Heat Deflection Temperature) and Vicat value, are negatively influenced. EP-A-0 264 143 describes the use of monosodium phosphate and disodium phosphate as stabilizers for mixtures of polybutylene terephthalate and polycarbonate. The invention is based on the discovery that a synergistic effect with respect to the crystallisation behaviour occurs when the combination of certain transesterification inhibitors and certain nucleating agents is used. The polymer mixture according to the invention comprises a transesterification inhibitor (C) selected from an inorganic pyrophosphate; an inorganic phosphate having at least two acid hydrogen atoms or an inorganic orthophosphate with crystal water or a mixture of one or more of these phosphates and talcum as a nucleating agent (D). The polymer mixture according to the invention comprises at any rate one or more of the following constituents: A. a first polyalkylene phthalate which comprises more than 35 mol% of units derived from 1,4-butanediol and which comprises more than 35 mol% of units derived from terephthalic acid; and B. B1 a second polyalkylene phthalate which comprises less than 15 mol% of units derived from 1,4- butanediol; or B2 a thermoplastic elastomer selected from a polyether ester block copolymer, a polyester ester urethane or a polyether imide ester or a mixture thereof, or B3 a mixture of B1 and B2; and C. a transesterification inhibitor selected from an inorganic pyrophosphate; an inorganic phosphate having at least two acid hydrogen atoms or an inorganic orthophosphate with crystal water or a mixture of one or more of these phosphates; and D. talcum as nucleating agent with the exception of polymer mixtures comprising 29.99 to 79.99 % by weight of the total composition of barium sulfate, strontium sulfate, zirconium oxide or zinc sulfate. In addition to the constituents mentioned hereinbefore, the polymer mixture may comprise any conventionally used additives. By way of example may be mentioned in particular polymeric additives to improve the impact strength, flame-retarding additives, reinforcing and non-reinforcing fillers, oxidation stabilisers, mould-release agents, processing additives, dyes and/or pigments. In addition, the polymer mixture may also comprise antimony oxide as an auxiliary agent, in particular when it comprises a flame-retarding additive, for example, a brominated aromatic carbonate-oligomer, -polymer or - copolymer. The weight ratio of constituent A to constituent B in the polymer mixture according to the invention preferably lies between 90 : 10 and 10 : 90, more preferably between 80 : 20 and 20 : 80. In the polymer mixture according to the invention constituent A may be, for example, a polybutylene terephthalate and constituent B may be a polyethylene terephthalate or a mixture of a polyethylene terephthalate and a thermoplastic elastomer, for example, a polyether ester block copolymer. A. The first polyalkylene phthalate Constituent A in the polymer mixture according to the invention is a polyalkylene phthalate which comprises more than 35 mol% of units derived from 1,4-butanediol and which comprises more than 35 mol% of units derived from terephthalic acid. In addition to 1,4-butanediol the polyalkylene phthalate may comprise units derived from one or more other aliphatic, cyclic or aromatic diol compounds or polyol compounds. In addition to units derived from terephthalic acid, the polyalkylene phthalate may comprise units derived from other dicarboxylic acids or polycarboxylic acids. A polybutylene terephthalate is preferably used as the first polyalkylene phthalate. B. Constituent B The polymer mixture comprises as constituent B B1 a second polyalkylene phthalate which comprises less than 15 mol% of units derived from 1,4-butanediol; or B2 a thermoplastic elastomer selected from a polyether ester block copolymer, a polyester ester urethane and a polyetherimide ester or a mixture thereof; or B3 a mixture of B1 and B2; and B1 is a polyalkylene phthalate which is not equal to constituent A. It comprises units derived from a diol compound and a dicarboxylic acid. In addition it may comprise units derived from polyol compounds and/or derived from polycarboxylic acids. Condition, however, is that the polyalkylene phthalate comprises less than 15 mol% (15 of the approximately 50 mol% of units derived from a diol which are usually present in a polyalkylene phthalate) of units derived from 1,4-butanediol. Suitable diol compounds are aliphatic, aromatic or cyclic diol compounds. B2. Thermoplastic elastomer The polymer mixture according to the invention may comprise one or more of the following thermoplastic elastomers. Polyether ester block copolymers are generally obtained by condensation polymerisation of one or more dicarboxylic acids, one or more long-chain glycols and one or more short-chain glycols. Examples of suitable polyether ester block copolymers are described in DE-C-2338615 and DE-B-2460258, as well as in the literature references mentioned therein. As a polyester ester urethane is preferably used a block copolymer which is built up from polyester ester units which are bonded by means of groups of the formula R1, [NHC(O)]p wherein R1 is a polyfunctional group having at most 30 carbon atoms and p has a value of 2 or 3. The polyester ester units are built up from blocks having a number of ester units of the formula - OGOC(O)R 2 C(O) - and blocks having a number of ester units which are capable of forming a bifunctional polyester or polyester amide having a melting-point of less than 100°C. These blocks are bonded together by ester bonds wherein at least 80 mol% of the R2 groups are 1,4-phenylene radicals and wherein at least 80 mol% of the G-groups are a tetramethylene group. Such polymers and their mode of preparation are described, for example, in EP-A-0102115, US-A-4,186,257 and US-A-4,228,249. As a polyether imide ester is preferably used a block copolymer obtained by reaction of a diol of low molecular weight, a dicarboxylic acid, a poly(oxyalkylene)-diamine and a tricarboxylic acid or a derivative thereof. Such polymers are described, for example, in US-A-4,544,734, US-A-4,556,705 and US-A-4,556,688, C. Transesterification inhibitor The polymer mixture according to the invention comprises a transesterification inhibitor selected from an inorganic pyrophosphate; an inorganic phosphate having at least two acid hydrogen atoms or an inorganic orthophosphate with crystal water or a mixture of one or more of these phosphates. Many transesterification inhibitors are known. In this connection reference may be made, for example, to the patent publications already mentioned hereinbefore. However, it has been found that the synergistic effect occurs when specific transesterification inhibitors are used as stated in the appended claims. Examples of suitable transesterification inhibitors which may be used in the polymer mixture according to the invention are inorganic pyrophosphates: for example, acid sodium pyrophosphate (Na 2 H 2 P 2 O 7 ), inorganic phosphates having at least two acid hydrogen atoms: mono zinc dihydrogen phosphate (Zn(H 2 PO 4 ) 2 ) mono calcium dihydrogen phosphate (Ca(H 2 PO 4 ) 2 ) inorganic orthophosphates with crystal water: zinc phosphate (Zn 3 (PO 4 ) 2 .2H 2 O) trisodium phosphate (Na 3 PO 4 .6H 2 O) Examples of very closely related transesterification inhibitors which, however, are not suitable, are: diammonium phosphate, dicalcium phosphate and dried zinc orthophosphate without crystal water. The transesterification inhibitor is preferably used in a quantity from 0.01 to 2 parts by weight per 100 parts by weight of A + B. D. Nucleating agent The polymer mixture according to the invention comprises talcum as a nucleating agent. Experimental investigations have demonstrated that other known nucleating agents, for example, sodium stearate and barium sulphate, do not show the found synergistic effect. The nucleating agent is preferably used in a quantity from 0.05 to 5 parts by weight per 100 parts by weight of the constituents A + B. In addition to the constituents mentioned hereinbefore, the polymer mixture according to the invention may comprise any constituent conventionally used for such polymer mixtures. The polymers which are generally known for improving the impact strength may be mentioned in particular. Herewith are meant in the first instance copolymers and graft copolymers which comprise rubber-like constituents. Examples are the core-shell graft polymers having a rubber-like core on which one or more monomers have been grafted. Examples of further suitable constituents for the polymer mixture according to the invention are the following: flame-retarding additives, reinforcing and non-reinforcing fillers, oxidation stabilisers, release agents, processing additives, dyes and/or pigments. The invention will now be described in greater detail with reference to the ensuing specific examples. The following constituents were used in the examples to be described hereinafter: A. PBT-1: a polybutylene terephthalate having an intrinsic viscosity of approximately 0.70 ml/g measured in a phenol-(1,1,2,2-tetrachloroethane) mixture 60:40 at 25°C. B. PET: a polyethylene terephthalate having a weight-averaged molecular weight of approximately 90,000. TPE: a polyether ester block copolymer having 44% by weight of polyether blocks and 56% by weight of polyester units. The polyether blocks are built-up units derived from polytetramethylene glycol and polyethylene glycol in a weight ratio of 85:15. The ester units are derived from butanediol, hexane-diol and terephthalic acid. Molar ratio butanediol to hexanediol is 70 : 30. C. ZP: Zinc phosphate with crystal water (Zn 3 (PO 4 ) 2 .2H 2 O) MAP: mono-ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) MZP: mono-zinc dihydrogen phosphate (Zn(H 2 PO 4 ) 2 .2H 2 O) SAPP acid sodium pyrophosphate (Na 2 H 2 P 2 O 7 ) DAP diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 ) D. T: talcum having a particle size smaller than 30 micrometres. Ba SO 4 : barium sulphate NaSt: sodium stearate Other: PE: finely ground polyethene GV: glass fibres having a length of 3.5-5.5 mm AO: an antioxidant on the basis of a hindered phenol UVA: a benzotriazole UV absorption agent. In the following examples, various polymer mixtures were prepared. The constituents used were compounded in an extruder (at a temperature adjusted on an average at 280°C) and pelletised. The glass fibres were fed laterally into the extruder. Test rods were injection moulded from the pellets. For Differential Scanning Calorimetry analysis, samples (approximately 10 mg) were cut from the said rods and then heated to 300°C (20°C per minute). The samples were then cooled (20°C per minute) and again heated. In the first heating the melting-points of constituent A and constituent B were measured (ml); upon cooling the crystallisation temperature Tc was measured and upon heating for the second time the melting-points of constituent A and constituent B were measured (Tm2). When the melting-points of constituents A and B after the second heating are shifted little with respect to the first heating, transesterification between the various polyesters has not occurred or has occurred hardly. A higher Tc value means in practice that the polymer mixture upon cooling crystallises sooner. This is of importance for the injection moulding cycle time. The sooner crystallisation occurs, the shorter becomes the said cycle time. Examples I to V and comparative examples A to F. The compositions as recorded in Table I hereinafter were prepared and examined by means of Differential Scanning Calorimetry. The results obtained are also recorded in Table I. Example Composition (parts by weight) A B C D E F I II III IV V A. PBT-1 39 37 37 37 39 39 37 37 37 37 37 B. PET - 38.1 38.1 38 38.1 38.3 38.1 38.1 38.1 37.7 - TPE 38.3 - - - - - - - - - 38.1 C. ZP - - - - - - - - - 0.6 - MZP - 0.2 0.2 - 0.2 - 0.2 - - - 0.2 MAP - - - - - - - - 0.2 - - SAPP - - - - - - - 0.2 - - - D. T - - - 2 - - 2 2 2 2 2 BaSO 4 - - 2 - - - - - - - - NaSt - 2 - - - - - - - - - PE 2 2 2 2 2 2 2 2 2 2 2 GV 20 20 20 20 20 20 20 20 20 20 20 A0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 UVA 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 DSC results (°C) Tml (PBT-1) 225 222 222 219 220 220 222 222 222 222 233 Tml (PET) - 248 248 249 250 250 248 250 250 250 - Tml (TPE) 225 - - - - - - - - - 233 Tc 184 174 188 179 181 164 194/203 190/198 190/198 187/193 200 Tm2 (PBT-1) 220 205 218 203 220 211 218 218 216 208 232 Tm2 (PET) - 218 240 226 245 229 240 237 237 230 - Tm2 (TPE) 220 - - - - - - - - - 232 Two different values of Tc means that constituents A and B crystallise separately. As may be seen from the results of Table I, the compositions of the comparative examples (A to F) have one value for Tc which is lower than both values of Tc of the examples according to the invention (I to V). This means that the combination of nucleating agent and transesterification inhibitor provides a Tc increase which exceeds that of the ingredients individually. Moreover, the polymers crystallise out separately when the above combination of nucleating agent and transesterification inhibitor is added. Example VI (for comparison) The synergistic effect as established for the polymer mixtures according to the invention did not occur in a mixture of two different polybutylene terephthalates (having different values for the intrinsic viscosity). Comparative example G The composition and the results are recorded in Table II hereinafter. Example Composition (parts by weight) G F A. PBT-1 37.4 39 B. PET 38 38.3 C. DAP 0.2 - ZP - - D. T 2 - Other PE 2 2 GV 20 20 UVA 0.25 0.25 AO 0.15 0.5 DSC results (°C) Tm1 PBT 225 224 Tm1 PET 250 250 Tc 175 170 Tm2 PBT 203 202 Tm2 PET 222 222 It may be seen from the results of Table II (comparative example G) that diammonium hydrogen phosphate (DAP) provides no essential change of Tc.

Claims: A polymer mixture comprising A. a first polyalkylene phthalate which comprises more than 35 mol% of units derived from 1,4-butanediol and which comprises more than 35 mol% of units derived from terephthalic acid; and B. B1 a second polyalkylene phthalate which comprises less than 15 mol% of units derived from 1,4-butanediol; or B2 a thermoplastic elastomer selected from a polyether ester block copolymer, a polyester ester urethane and a polyether imide ester or a mixture thereof; or B3 a mixture of B1 and B2; and C. a transesterification inhibitor selected from an inorganic pyrophosphate, an inorganic phosphate having at least two acid hydrogen atoms or an inorganic orthophosphate with crystal water or a mixture of one or more of these phosphates; and D. talcum as nucleating agent with the exception of polymer mixtures comprising 29.99 to 79.99 % by weight of the total composition of barium sulfate, strontium sulfate, zirconium oxide or zinc sulfate. A polymer mixture as claimed in Claim 1, wherein the weight ratio between constituents A and B lies between 90:10 and 10:90. A polymer mixture as claimed in Claim 1, wherein the polymer mixture comprises 0.01 to 2 parts by weight of constituent C per 100 parts by weight of constituents A + B. A polymer mixture as claimed in Claim 1, wherein the polymer mixture comprises 0.05 to 5 parts by weight of constituent D per 100 parts by weight of constituents A + B. A polymer mixture as claimed in Claim 1, wherein constituent A is polybutylene terephthalate and constituent B is polyethylene terephthalate. A polymer mixture as claimed in Claim 1, wherein constituent A is polybutylene terephthalate and constituent B is a polyether ester block copolymer. A polymer mixture as claimed in Claim 1, wherein the polymer mixture comprises in addition to the constituents mentioned hereinbefore a polymer to improve the impact strength. A polymer mixture as claimed in Claim 1, wherein the polymer mixture comprises in addition to the constituents mentioned hereinbefore one or more of the following additives: flame-retardant additives, reinforcing and non-reinforcing fillers, oxidation stabilisers, release agents, processing additives, dyes and/or pigments. Articles formed from the polymer mixture as claimed in Claim 1.

Inventors: HEUSEVELDT JAN WILLEM, KETELS HENDRIKUS HUBERTUS THEO, VAN HELMOND JOHANNES, HEUSEVELDT, JAN WILLEM, KETELS, HENDRIKUS HUBERTUS THEODOOR MARIA, VAN HELMOND, JOHANNES
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1994
Main classification: C08L67
IPC codes: C08K3, C09D175, C08L75, C08L79, C08L67